Current rectifier



E. FRIEDERICH ET AL CURRENT RECTIFIER Filed Sept. 18. 1928 Patented Dec. 31, 1929 UNITED STATES PATENT OFFICE ERNST FRIEDERICH AND WILFRIED MEYER, 0F BERLIN, GERMANY, ASSIGNOR TO :PATENT-TREUHAND-GESELLSCHAFT FUER ELEKTRISCHE GLUEHLAMPEN M. B. H.,

0F BERLIN, GERMANY CURRENT nnctririnn Application led September 18, 1928, Serial No. 306,679, and in Germany September 30, 1927.

Our invention relates to improvements in electric current rectifiers, and more particularly to rectiiers ot the type comprising a couple of the dry surface-contact variety, being an improvement of the rectifiers described in our co-pending application, Serial No. 287,873, i'iled June 23, 1928.

In such rectiliers comprising several lay- 'ers of ditlerent materials one of which at least conductive compound, the layer of the poorly conductive compound in contact with a metal or a conductive metal Compound, must not exced a certain thickness because a too great drop of tension will result. Such a current rectiiierat high tensions will scarcely pass any current.

It is exceptionally diilicult to make such very thin films mechanically. L

It has been proposed to overcome this diiiiculty by electrolytically coating one of .the plates of a current rectiiier before assembling, with an oxide, or after assembly of the rectifier to coat the plate on which the poorly c onductive coating is to be made by interposing a thin' layer of water, and then upon the passage of the current decomposing the water. The products ot decomposition of the water reacting with one of the plates to -torm a poorly conductive coating of oxide or hydroxide.

We have discovered that the ditlicult mechanical method, as well as the time consuming electrical method of making the rectifying layer or coating may be easily avoided.

This we` do by making the parts of the current rectifier, between which the poorly conis a layer of a poorly lductive layer shall lie, of materials that shall react with one another, and between which the poorly conductive layer is to be formed so that this layer of reaction compound shall contain products of both layers. v For this purpose, in general, two chemical compounds shall be used, at least one of which is comparatively poorly conductive. The resulting non-conductive layer can be so exceptionally thin that itscannot be determined by the usual analytical methods. It must, however, be present as the two materials in contact with one another,

. iodide containin according to the chemical faces of these two materials there results in' presence of the excess iodine, thepoorly conductive iodide of lead (PbIz) In many cases the materials that form the non-conductive layer of lead oxide will react at atmospheric temperatures. In other cases, however, it is advantageous to assist the reaction by external heat or with the assistance of directk or alternating current or by heavy pressure. The rapidit of the reaction can be increased by using allI of these methods for causing the reaction, at the same time. The drawing illustrates a cross section of an element comprising a lead plate a, an intermediate layer of cuprous iodide c containing preferably an excess of iodine d and a copper plate e. cated at b. l

The lead plate in contact with the layer of copperv iodide containing iodine will react to form lead iodide PbI2.

We claim- 1. A dry, surface-contact current rectifier, comprising a conductive layer of cuprous iodide containing free iodine, a lead plate and an intermediate poorly conductive layer of lead iodide.

2. A dry, surface-contact current rectifier, comprising a conductive plate covered with cuprous iodide containing free iodine, a lead plate and an intermediate film of lead iodide The rectiying layer of PbIz is indiproduced by the reaction betwen the cuprous and an intermediate ilm of lead iodide produced by the reactionv between the cuprous free iodine and the lead. v In testmonyt at we claim the foregoing as our invention, we have signed our names ERNST FRIEDERICH. lVVILFRIED MEYER hereto. 

